Yeah, maybe pass the info on. If I get a board built and the circuit works as it should then I will likely have a number of these made (which will probably sit around my house forever) in case someone would want to buy one.

Ideally I would like to find someone who could make the boards but also assemble it all as a kit including all the components needed, but I could probably do that myself if I ever get to the board making stage

BTW, I'm adding a titleblock to the design, and wondering whom else to add to the designed by section. IE, Jman, is that the name I should list there? I must include those who have contributed and added to the design, namely also because you are selling the product of which I used a portion in my design if I'm not mistaken, the purpose is just different.

But you did end up giving me another idea, of adding a another output(s) specifically to drive LED strips like you have.

It would be independant of my amplifier circuit, but would rely on the outputs of the op-amps to be triggered so would just be like a port that you could plug the LED driver circuit into.

the output on my box would be signals from the pads that would then plug into another box containing the 555's and circuitry to drive the LED strips.

mind I'm going to get a working prototype of my circuit done first before I go getting all nuts.

I'm not worried about any credits on this. the circuit was a collaboration of several peoples ideas anyways. If you decide to add an LED output, you will want to have a look at my LED circuit. The circuit I gave you drives the LED directly off the timer chip. you really need to drive a transistor that will switch the leds on and off.

I'm not qorried about that quite yet anyway, I have a couple of other things to do. I still need to add in some ports for allowing the addition of 3 more cymbals to the kit, and figure out what needs to be done so two modules can be plugged into the box, and share a common output. It isn't quite as simple as just splitting them from what I understand.

I would like to also have a decent power supply to keep the rails balanced because there are a quite a few things being powered from positive and really nothing on the negative side. I really don't know if it would cause problems in this application, but I was thinking of maybe using a zener or something for regulation.

If add the ability to drive LEDs it will definitely require a wart.

How do I go about figuring out the current requirements for my circuit in a worst case scenario. We've done this in school but a bit differently since we werent using an AC input to the op-amp and this won't even be close to a sine wave in real life so the only power being drawn is by the op-amps, LED's, Timer, JFETs? and a reed relay for another purpose.

The best place to get current requirements for components is from their data sheets. I get almost all of my components from Mouser and they always have the data sheets linked to their components. Sometimes it's tough to understand them but it should be there.

I dont think they have any power supplies for loan, but I didn't ask.....yet.

I was going to use LM78/79 regulators but it was either here in one of my threads, or another board that mentioned it would be useless because the 9V battery isnt the right voltage for a 9V regulator, and so it won't give me 9V out.

I wanted to use them so that if the batteries were dying, the regulators would simply stop working when the batteries got too dead, instead of the circuit doing weird things because the voltage is too low.

could I use 7812's and connect 2x9v batteries in such a way as to provide 18V to the 7812's?

You could, or you could use a 12V battery pack to power the 7809s.Note than the 78xx/78xx line of regulators will have no issues with unbalanced loads, provided that the total current capabilities of the regulators are not exceeded.Note also that they have a minimum operating current of ~15ma. I usually us an LED as a power indicator, running from the regulator, to ensure that this minimum load requirement is met. However, anything between 15ma & 1000ma load current will give you a nice constant regulated voltage.

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Trouble rather the tiger in his lair, than the sage among his books.For to you, kings & armies are things mighty & enduring.To him, mere toys of the moment, to be overturned at the flick of a finger.

While checking in multisim I think as a bare minimum I would need 200mA, and maybe 400mA just to be safe and have some headroom.

I was considering a battery pack, but they all seem fairly expensive, but when I look at the number of parts I'll need for the end product I can see it isn't going to be a super cheap device Where can I find a 12V battery pack with +/- voltages?

Either that or how the heck do I build a rail splitter, I've been searching my face off and haven't really turned up any relevant designs or something that DOESN'T use a MAX1044.I'm trying to use easily(locally?!) available parts.

heh ... you really don't want to split a single sided supply for this device .man , that is engineering a problem into a circuit .

400mA ... yep , that is asking a lot from a 9 volt battery .

two rechargeable battery packs is a simpler solution .you will need the associated charging regulation/monitoring circuitry whether or not the packs are built in or removable .

questions ...can this device be "line powered" or is it essential that the primary use of batteries is to afford "portability" ?is the device to be used continuously/active for a fair amount of time or is it more of a diagnostic tool ?

Battery power is important, but like I said before, the device won't actually be always on. 400mA is if everything is turned on and running continuously.

As it is, when one drum pad is it, it will only register a tiny flash from the LED, and the op-amps will only be dealing with pulses.

Portability is big because this will be mounted to a drum set, that doesn't have any access to a nearby outlet, so plugging it into the wall would be a real pain, especially as t he drum set is moved frequently.

Using low power op-amps will save a lot, as will avoiding the use of resistor dividers to generate voltages (like splitting a supply). Should be able to get current consumption down to a few mA total at idle, and the flicker from LEDs blinking will only be a few mA on top of that, momentary. Incidentally, remember superbright LEDs make excellent indicators at reduced current -- at 20mA or whatever, they're blinding, but at 1mA or so they're quite acceptable indicators (whereas diffused garden variety LEDs take 20mA for the same intensity).

Tim

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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.

I dont think I have any resistor dividers except on the op-amps as required. And I may want to bump those down from 180k/100K to around 2K.....that is if I understand the datasheet correctly, but even then my understanding may be off.

Anyway the 358's (LM324) are low power are they not? And you're saying I should use ultra bright LEDs as the indicators because they will also show me when the battery is getting low?

There are lower current devices than LM324 -- it was "low power" back in the 70s. CMOS chips are pretty good these days; ironically, TLV2371 draws about as much supply current as LM324, so despite its age it's not even that bad in the grand scheme of things.

I recommend high brightness LEDs because you can run them at lower current, increasing battery life. They're just LEDs, nothing special about them.

If you want a "low battery" indicator, you can add a battery monitor -- there are single chips that do this (although most of them are for cellphones and come in grain-of-sand DFN packages!), or you can add a comparator (heck, might as well be LM393 -- basically an LM358 without the analog output stage!), voltage reference (TLV431 is low enough current, or you can choose one of many low current chips; I wouldn't recommend using a zener diode as they are particularly noisy at low current).

If you have, say, eight channels in this thing, using four chips total, you'll draw about 2mA by idle power, plus maybe double that, counting all the resistors, loads, etc. 4mA will last a ~200mAh "9V" battery for 50 hours -- two days continuous use, or several weeks if used a couple hours per session.

Tim

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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.

There are lower current devices than LM324 -- it was "low power" back in the 70s.

I dig.....

I was just gonna put an LED across the rails with a 1.8K or 2K resistor for an on/off indicator.

I didn't know battery monitors came in a single chip, I may look into it, but a battery level indicator isn't that important, and I've seen quite a few designs for them. I am still considering using a battery pack with a charging circuit, and adding a plug to let it run from wall power.

Before I go about doing that though, I would like to find a simple but viable solution for this circuit to run it from no more than 2x9V batteries just so I can get one or two of these made test it out and then make further revisions if nessecary.

There are 8 channels using 2xLM324's. 1 channel per amp and each drum strike only lasts 10ms, and in worse case scenario I think there would only be a maximum of 12 hits per second, so a total in use time of 40ms per second. (do you know anyone who can hit 8 drums at the same time, each 4x per sec? cause that would be awesome) I say 40ms because those 12 hits are being done by 3 limbs for 3 drums, each drum being struck 4x per sec.

For a battery monitor, you compare a fraction of the supply voltage with a reference voltage. When Vcc/2 (say) > Vref, the battery is good. Note that, when Vcc is really low (less than Vref or so), Vref will also fall (and no longer be a ref as such); but this is okay, because the fraction (Vcc/2 or whatever) is still lower than whatever Vref drops to, and the comparator remains off.

Example:http://webpages.charter.net/dawill/tmoranw..._Gate_Drive.gifThe bottom left section contains a 5V reference (4.7k resistor, zener diode), adjustable fraction of the supply voltage (10k trimmer, 'UVLO ADJ'), some positive feedback (the 10k and 100k on the comparator) and a logic level output (the 4.7k going up into the circuit; this could be a simple LED for a power monitor). "UVLO" stands for Under Voltage LockOut, because this circuit keeps itself disabled until its supply voltage is high enough for guaranteed operation.

Tim

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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.

The comparator only pulls down (although I've seen Multisim models where they neglect to un-opamp-ifiy the stupid things and they drive current anyway), so the loose end of the 4.7k should be to a positive voltage source (0V or +9V), or a load (like a transistor base, or an LED).

That zener will be running pretty hot with 4.7 ohms.

As shown, you have two means of demonstrating behavior:1. During an interactive simulation, vary the pot and watch at what percentage it flips. There should be some hysteresis (i.e, starting at 100% and going down, maybe it flips at 45%, and stays flipped until you go up to 55%), but the amount may be too small to see (in which case, change the percentage increment to something smaller, or use a different analysis).2. Choose a DC sweep analysis, varying V1 as the parameter from -9V (i.e., so the total supply starts at 0V) up to 9V in, say, 201 steps. As simulation output, select the comparator output node voltage (it's probably automatically named, double click the net to see what it's been named as, or to rename it if you prefer -- a good idea), or the current flow in R59. This will only observe the rising threshold.

3. This isn't as shown, but you can change R57 wiper to a voltage source (e.g., use the function generator with a triangle wave) to sweep the voltage slowly (<1kHz) and note where the output changes state. Alternately, do the same thing with V1 replaced by the generator instead. (This probably isn't a physically realizable solution, but don't worry: simulation sources have zero output resistance; Multisim doesn't care that your bench function generator actually has a 50 ohm source resistance!)

At any rate, however you vary and measure the parameters, if you're varying R57, measure the voltage at the wiper when it's at the desired threshold (i.e., ser V1 + V2 to the minimum voltage and adjust R57 until it just turns off); this will tell you what voltage ratio you need. R57 can then be replaced with a (fixed) resistor divider. Alternately, leave R57 fixed at a known ratio, and vary V1+V2 until you've found the threshold. Divide by the desired threshold to find the actual ratio required. Or just do it by design -- the BZX85-C5V1 has a well-defined V/I characteristic, so you can calculate what voltage it develops at the threshold, given however much bias. Calculate the ratio of R57 so that the divided voltage equals the reference voltage, i.e., Vcc(min) * R57(bottom) / (R57(total)) = Vref (where R57(bottom) means the resistance of the bottom half, from wiper to ground).

Again, D9 can be replaced by any number of micropower voltage references; TI/National, LT, AD and everyone else make references in any quality you'd want. A simple, low current shunt type reference will suffice here.

Tim

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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.